Electric discharge lamp



Patented Feb. 7, 1939 UNITED STATES ELECTRIC DISCHARGE LAMP George E. Inman, East Cleveland, Ohio, assignor to General Electric Company, a corporation of New York Application April 22, 1936, Serial No. 75,772

4 Claims.

My invention relates to gaseous electric discharge lamps and has for its object the provision of a lamp having novel and improved structural features.

According to my invention, the lamp comprises a tubular glass container having a metal disc sealed to each end thereof with an electrode mounted on each of said discs and electrically connected thereto. The discs are shaped to engage with suitable holders for mounting the lamp, thereby serving as engagement and contact means as Well as end walls for the container. Moreover, the discs permit the lamp to be lighted substantially to its very ends which is particularly advantageous where the lamps are mounted end to end to form a line of light. makes easier the application of powdered materials such as luminescent materials to the inner surface of the container, since the powder may be readily applied to the tubular container before the end discs are sealed thereto. Further features and advantages of my invention will appear from the following detailed description of species thereof and from the drawing.

In the drawing, Fig. l is a side elevation, partly in section, of a lamp comprising my invention; Fig. 2 is an elevation showing in detail a portion of one of the electrodes; Fig. 3 is a detailed perspective view of the supporting structure for an electrode; and Fig. 4 is a side elevation, in section, of an end of a lamp having a modified electrode structure.

Referring to the drawing, the lamp comprises a tubular glass container I0 having a metal disc I I sealed directly to each end thereof and serving as an end wall and contact. The discs Il are of the type shown and claimed in the U. S. patent application to Harold D. Blake, Serial No. 3,344, led January 24, 1935, and may be made of an iron alloy containing about twenty-nine per cent of chromium, such as an alloy marketed by the Allegheny Steel Company as Allegheny 55. The discs are preferably concave or dish-shaped as shown so that they may be made of thin material and still be adequately strong. The said discs I I each has an annular recess or depression I2 at the center, preferably of an inverted conoidal form, that is, it preferably increases in diameter inwardly from the edge or surface of the disc forming a circular groove I2' therein. The recesses I2 are adapted to be engaged by resilient portions of suitable holders which snap into the depressions in the manner of glove fasteners. One of the discs has an opening I3 at the center of the recess I2 through which the container I0 is exhausted and filled with a suitable gas or gases, the said opening I3 being subsequently sealed by fusion of the residue I4 of a glass exhaust tube.

A pair of electrodes I5 are located at the ends of the container I0, each of said electrodes con- Such a construction also sisting of a filament I6 of refractory metal, preferably tungsten, coiled around a mandrel I1, also preferably of tungsten, the coil on mandrel being again coiled as shown at I8. The portion I8 of the electrode is covered with a coating, indicated by the dots at I9, of an electron emissive material such as barium oxide. The straight end portions 20 of the electrode are attached, preferably by welding, to the transversely extending end portion 2l of a support member or wire 22, the other end 23 of which is in the form of a resilient split ring encircling the boss or shoulder formed at the inside of the disc II by the recess I2 and lying in the groove I2. The electrodes I5 are thereby electrically connected to the discs I I through the supports 22.

The container I0 has a starting gas therein such as argon at a pressure of about 4 mm. and a quantity 24 of vaporizable metal, preferably .002 to .003 c. c. of mercury. During the operation of the device the electrically excited mercury vapor emits visible and ultra-violet light. For ease of starting, a strip 25 of conductive material such as a metallic paint or graphite mixed with potassium silicate is applied to the container I0 and is in contact with one disc I i and extends to a position adjacent the electrode I5 at the opposite end of the container. The said strip 25 is of high resistance, preferably about 50,000 ohms or more.

The inner surface of the container applied thereto a coating 26 of luminescent material such for example as zinc silicate, cadmium silicate, cadmium tungstate, or some specially prepared materials such as a mixture described and claimed in the U. S. patent application Serial No.

75,783, Willard A. Roberts, of even date, and consisting of about sixty parts of CdO, forty parts of SiOz and a small amount of manganese, or another mixture described and claimed in the U. S. patent application Serial No. 75,780, Willard A. Roberts, of even date, and consisting of about sixty parts of ZnO, forty parts of SiOz and a small amount of manganese, or still another mixture described and claimed in the U. S. patent application Serial No. 75,782, Willard A. Roberts, of even date, and consisting of CaO and W03 in such proportions that there is from one to ten per cent more calcium oxide than is required by the chemical formula Ca'WO4, with or Without a small amount of lead. The coating 26 of luminescent material may be applied to the surface of the container ID by means of a binder, or it may be embedded in the glass itself by heating the glass to its softening point or, if the powdered material is fine enough, it will adhere by merely dusting it into the container. The powder may also be mixed with a binder and sprayed on the container. Among the various binders which may be used are glycerin; glycerin and twenty per cent of borc acid; phosphoric acid alone or diluted with ace- ID has tone or alcohol; potassium silicate; an ester of glycerin with boric acid; castor oil or mineral oil; or an inorganic resin such as that sold under the name of Stacol by the Glyco Products Company, Inc., of Brooklyn, N. Y;

The luminescent powder may be applied to the container I before the discs I I are sealed thereto in the following manner:

A cork or stopper is inserted in one endiof the container, an excess of binder (such as a mixture of 5 c. c. of eighty-five per cent HaPO4 and 40 c. c. of methyl alcohol) is poured in, a cork is inserted in the other end of the container and the container is shaken to distribute the binder over the inner surface thereof. The excess binder is then poured out and the container is set vertically and allowed to stand for about fifteen minutes. Next a dry sponge covered with a double layer of iine mesh cheesecloth is drawn back and forth through the container to remove the excess binder. This operation maybe repeated with clean cloths to obtain minimum streaking and yet leave suiicient binder for the proper coating thickness. then be set at an angle of about thirty to sixty degrees with a clean receptacle at the lower end thereof and the luminescent powder poured in at the top while the container is being rotated. 'Ihe ends of the container may then be reversed and this operation repeated. The container may then be held vertically and jarred at the ends to remove the excess powder. The container is then heated for about fteen minutes at a temperature of about 425 to 450 C. to remove the volatilizable portion of the binder and fuse the remainder. The containers are now ready for the sealing of the discs H thereto with the electrodes attached.

During the operation of the lamp the ultraviolet rays striking the luminescent material are transformed thereby into visible light rays which complement and supplement the spectrum of the visible light emitted by the electrically excited gaseous atmosphere. A 15 watt lamp of the type shown having a container about one inch in diameter and about eighteen inches long requires a starting voltage of about 250 volts. The lamp operates at about 65 volts and one-quarter ampere. 'I'he lamp therefore operates at a current density of about .05 ampere per square centimeter of cross section and with an energy consumption of about .04 watt per square centimeter of container surface. The lamp may be operated simply by a leakage transformer by connecting the discs II to the secondary thereof.

The low pressure mercury arc in the lamp described produces short ultra-violet radiation with very high eiiiciency, about fifty per cent of the wattage input to the lamp being converted into radiations of 2537 angstroms. These radiations are very eflicient in exciting iiuorescent light from phosphors such as zinc silicate, cadmium silicate and calcium tungstate'. Efficiencies of 74 lumens per watt have been obtained in lamps of the type described using the special zinc-silicon-manganese phosphor described above, 26 lumens per watt with the special cadmium-silicon-manganese phosphor and 22 lumens per watt with the special calcium-tungsten-lead phosphor.

Fig. 4 shows a modif-led end and electrode structure. The electrode 21 may be of the type described and claimed in U. S. Patent application Serial No.16,614, Eugene Lemmers et al., filed April 16, 1935, and consisting of a porous body of refractory metal, such as tungsten, impregnated The container may with an electron emissive material such as barium oxide. The said electrode 21 is mounted on one end of a support wire 28, the other end of which is secured. preferably by welding, to the disc l l. 'I'he inner surface of the disc I I, and the support wire 28, may also be covered by insulating material 29, such as a glaze.

While I have shown and described and have Pointed out in the annexed claims certain novel features of the invention, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its use and operation may be made by those skilled in the art without departing from the broad spirit and scope of my invention. For example, the ends 20 of the electrode I5 in Fig. 1 may be spot welded directly to the disc I l, thus eliminating the supporting member 22, and the inner surfaces of the discs H in the lamp shown in said Fig. 1 may be coated with insulating material.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A gaseous electric discharge lamp comprisimg a tubular glass container, a metal disc sealed directly to each end of said container as an end wall and contact, each of said discs having a depression therein for engagement with a holding means forming a peripherally grooved boss at the inside thereof, a, conductive support member encircling the said boss on each of said discs and lying in said groove and extending a short distance therefrom, and an electron emissive electrode mounted on each of said support members in front of the adjacent disc and electrically connected through said support member to the said adjacent disc.

2. A gaseous electric discharge lamp comprising a tubular glass container, a metal disc sealed directly to each end of said container as an end wall and contact, 'each of said discs having a. depression therein for engagement with a holding means forming a boss peripherally grooved at the inside thereof, a conductive support member encircling the said boss on each of said discs and lying in said groove and extending a short distance therefrom transversely of the container, and an electrode at each end of said container comprising a coil of refractory wire having its ends secured to the transversely extending portion of said support member and electrically connected therethrough to the adjacent disc.

3. A gaseous electric discharge lamp comprising an elongated tubular glass container having a filling of inert'gas and metallic vapor and having sealed across each of its ends a metal closure disc, a support wire secured to saiddisc and extending forwardly thereof, a thermionic electrode supported from said wire, and a coating of insulating material over the interior surface of the disc and over the wire, said coating insulating said disc and Wire from the gas filling inside the lamp.

4. A gaseous electric discharge lamp comprising an elongated tubular glass container having a filling of inert gas and metallic vapor and having sealed across each of its ends a metal closure disc with an inward peripherally grooved boss, a wire encircling said boss and lying in said groove, a thermionic electrode supported from said wire, and a coating of insulating material over the interior surface of the disc insulating said disc from the gas filling in the lamp.

GEORGE E. INMAN. 

